1. Field of the Invention
An embodiment of the present invention relates to an apparatus for image reading and a method for setting the image reading. The apparatus and the method are suitably applied to an image reading apparatus for optically reading an original by a scanner, and also suitably applied to a digital copying machine for forming an image on the basis of read image data, etc.
2. Description of the Related Art
A 3-line CCD sensor constructed by three lines of RED, GREEN, BLUE has been hitherto adopted as an optical sensor for color image reading. The 3-line CCD sensor is designed so that color filters of RED, GREEN, BLUE are disposed on respective light receiving faces of three line sensors, and the three line sensors are arranged in parallel.
Recently, 4-line CCD sensors have been commercially produced. The 4-line CCD sensor is equipped with a monochromatic reading line sensor for reading a monochromatic image in addition to the 3-line CCD sensor. In the 3-line CCD sensor, each of the line sensors has a color filter that transmits only light having a specific wavelength therethrough and disposed on the corresponding light receiving face. In comparison with the 3-line CCD sensor, the monochromatic reading line sensor has no color filter disposed on the light receiving face thereof. Japanese Patent Application Publications (KOKAI) No. 2004-272840, No. 2004-180196 and No. 2003-274115 are known as documents showing techniques relating to CCD sensors.
In the 4-line CCD sensor, the four line sensors are disposed so as to be spaced from one another at intervals in the scanning direction of an original. Therefore, it is impossible that all the line sensors simultaneously read the same place of the original. Furthermore, it is impossible to match the focal point of a condenser lens to all the line sensors at the same time.
Therefore, according to the image reading apparatus having the 4-line CCD sensor, focus adjustment for images to be read by the RGB line sensors for color is carried out, and then focus adjustment for an image to be read by the monochromatic line sensor. When the focusing state achieved when the image reading is carried out by the color RGB line sensors is caused to be out of focus by the focus adjustment for the image to be read by the monochromatic line sensor, the focus adjustment when the image reading is carried out by the color RGB line sensors is carried out again. As described above, such balanced adjustment that the focusing conditions for both color and monochrome are set to averagely optimal focus positions is repetitively carried out.
However, the above-described method increases the adjustment time because of repetitive re-adjustment and also requires the adjustment to set the focusing positions for both the color and monochrome to the averagely optimal ones, so that the adjustment concerned finally sacrifices the image performance inherent to the lens.